This invention relates to ultrasonic probes for diagnostic examinations and especially to a wear plate at the front surface of the transducer array which contacts the human body. This probe also can be used for water tank testing.
All transducer arrays in medical ultrasound instruments need a smooth continuous surface for body contact. The array itself is rough because of the slots between individual elements and a smooth covering is required. Furthermore, since some arrays represent a fragile architecture, a stabilizing material preventing damage at nominal body contacting pressures must be placed on the front surface.
Many commercial ultrasonic probes have wear plates with undesirable acoustic properties. An epoxy-like material has been used as an acoustic impedance matching layer and as a wear plate, and while this material is extremely rugged and mechanically strong, the high velocity of sound in the epoxy and its continuous surface result in refraction of acoustic waves away from the transducer elements. This results in a severely restricted field-of-view for the individual elements as shown in dashed lines in FIG. 6.
The requirement of an improved array covering is essential in a steered beam imager with a wide scan angle of about 60.degree. to 90.degree. using an array of narrow elements having a width on the order of one wavelength or less at the ultrasound emission frequency. Assuming that the beam is steered at a maximum angle of 45.degree. from a normal at the center of the array, refraction of acoustic waves in the wrong direction during reception or transmission cannot be tolerated and leads to degraded performance.